A seat belt retractor having a tension eliminator comprises a belt take up shaft, a return spring, a first rotatable member rotatable together with the belt take up shaft, a second rotatable member rotatable about the first rotatable member, the relative rotation between the first and second rotatable members being restricted, a spiral spring for biasing the first and second rotatable members to rotate in opposite directions, a stopper device for causing the second rotatable member to take a one-way rotatable condition, a completely locked condition and a released condition, a control device for controlling the stopper device so that when the first rotatable member rotates in one direction, the second rotatable member under the first condition is brought into the third condition and when the first rotatable member rotates in the other direction, the second rotatable member under the third condition is brought into the second condition, and a buckle switch for controlling the stopper device so that when the belt takes the seat occupant restraining position, the second rotatable member takes the first condition.